CodeForcesGym 100735D Triangle Formation

Triangle Formation

Time Limit: Unknown ms

Memory Limit: 65536KB

This problem will be judged on CodeForcesGym. Original ID: 100735D
64-bit integer IO format: %I64d      Java class name: (Any)

 

You are given N wooden sticks. Your task is to determine how many triangles can be made from the given sticks without breaking them. Each stick can be used in at most one triangle.

 

Input

The first line of each test case contains the number of sticks N. (1 ≤ N ≤ 15)

The second line of each test case contains N integers leni that are the lengths of the sticks. (1 ≤ leni ≤ 109).

 

Output

Output single integer R – the maximal number of triangles.

 

Sample Input

Input

2
1 1

Output

0

Input

3
2 2 2

Output

1

Input

6
2 2 3 4 5 6

Output

2

Source

KTU Programming Camp (Day 1)

 

解题：状压

#include <bits/stdc++.h>
using namespace std;
const int maxn = 20;
typedef long long LL;
int dp[1<<maxn],n;
LL a[maxn];
int main() {
    while(~scanf("%d",&n)) {
        for(int i = 0; i < n; ++i) scanf("%I64d",a + i);
        sort(a,a+n);
        memset(dp,0,sizeof dp);
        int ret = 0;
        //cout<<"n:"<<n<<endl;
        for(int i = 0; i < n; ++i) {
            for(int j = i + 1; j < n; ++j)
                for(int k = j + 1; k < n; ++k) {
                    if(a[i] + a[j] > a[k]) {
                        //cout<<"ok"<<endl;
                        for(int t = 0; t < (1<<n); ++t) {
                            if(((t>>i)&1) || ((t>>j)&1) || ((t>>k)&1)) continue;
                            int tmp = (t|(1<<i)|(1<<j)|(1<<k));
                            dp[tmp] = max(dp[tmp],dp[t] + 1);
                            ret = max(ret,dp[tmp]);
                        }
                    }
                }
        }
        printf("%d
",ret);
    }
    return 0;
}